Large cooling towers, such as those used by power plants, are used to cool water by convective, counter flow, direct heat transfer with a rising air column. Typical cooling towers, vertical axis upflow venturis constructed of concrete, are elevated on columns providing a circular, horizontal entrance area at the base of the venturi draft channel of about 300 ft. to 350 ft. in diameter that enables air to flow horizontally in under the elevated entrance area and rise upward to the open top area of the tower.
Typically within the lower third of the 400 ft. to 500 ft. high venturi draft channel axial length (height) and across the 300 ft. to 350 ft. draft channel horizontal entrance section, a 10 ft. to 20 ft. thick section of porous fill material is provided to receive a sprayed distribution of the hot process water to be cooled by the tower. This fill material usually is thin plastic membrane formed in packed bundles of vertically disposed, small diameter tubes similar to a honeycomb structure. Water sprayed over the top face plane of the fill attaches to the tube walls as a thin liquid film, flowing downwardly while air rising through the open space within the tubes convectively extracts the water carried heat. As the air absorbs heat, it expands to reduce the specific density thereby buoyantly rising while fresh, cooler and more dense air flows from below to fill the evacuation, be heated and continue the open cycle.
From the lower face of the porous fill material, the cooled process water falls in the manner of a heavy rain over a vertical height of about 50 feet into a collecting basin. Through this heavy rain, fresh atmospheric air is first drawn laterally by the lower end of a low pressure axial column of rising air. As the laterally flowing air penetrates the rain, residual heat in the rain water transfers to the cooler air thereby beginning the air flow turn up the venturi draft channel.
Although very efficient, the aforedescribed structure and system remains with considerable opportunity for improvement due to an uneven water temperature gradient across the draft channel suction. Water falling into the basin from around the outer rim annulus of the draft channel is substantially cooler than water falling along an axially central column. As supply air radially penetrates the cylindrical cross-section volume beneath the lower venturi rim from the exterior perimeter, the rainfall restricts, heats and slows the radial air flow which results in a disproportionate loading of the incoming air heat absorption capacity with outer rim heat, thereby leaving the central core of the venturi with a smaller heat exchange differential between the air and water. The final temperature of process water falling into the basin from a central core area is hotter than the water falling from the outer perimeter.
It is therefore, an object of the present invention to provide a protective air flow shield which permits a predetermined proportion of fresh atmospheric air to penetrate the falling water zone of a natural draft cooling tower and reach the internal core of the draft channel without having to overcome outer perimeter rain resistance and heating thereby providing additional cooling and lower exit water temperatures.
Another object of the present invention is to lower the average temperature of cooled process water from the basin of a natural draft cooling tower.
Another object of the present invention is to provide a smaller variation in the range of cooled process water temperatures entering the basin of a natural draft cooling tower.
Another object of the present invention is to increase the overall thermal efficiency of a power production facility associated with a natural draft cooling tower.
Another object of the present invention is to provide a reduced heat rate (BTU/kw-hr.) of a power production facility associated with a natural draft cooling tower.
Another object of the present invention is to reduce the environmental impact of power production facilities due to increased thermal efficiency and correspondingly decreased heat rate.
Another object of the present invention is to provide a natural draft cooling tower with increased process water flow rate capacity for a given exit water temperature.
Another object of the present invention is to provide a device that is readily retrofittable to existing cooling towers.
A still further object of the present invention is to provide increased cooling air flow rates for natural draft cooling towers by reducing the cooling air pressure losses and the highest exit air temperatures.